Neptunium behaviour in PUREX and GANEX processes

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1 Neptunium behaviour in PUREX and GANEX processes C. Gregson, M. Carrott, D. Woodhead, R. Taylor SNEC 2014, Manchester

2 Challenges in Np separations chemistry Background Neptunium extraction in an Advanced PUREX process Neptunium extraction in a GANEX process

3 Options for future fuel cycles R: Recycle plant FR: Transmutation reactor V: Vitrification FR MA U, Pu R V FP FR R U, Pu, MA V FP Heterogeneous Recycling Homogeneous Recycling Advanced PUREX + DIAMEX-SANEX or EXAm GANEX

4 Requirements for advanced reprocessing Optimise recycling processes so the option to close the fuel cycle by ~2050 is competitive with other spent fuel management options Reduced costs Reduced wastes Reduced environmental impact Enhanced process safety Enhanced proliferation resistance / safeguards Enhanced public acceptability Flexibility to process wider range of fuel types Integrated with fuel fabrication and waste management PROCESS SIMPLIFICATION / INTENSIFICATION / INNOVATION

5 Neptunium

6 Np in the fuel cycle Current closed fuel cycles Np in HLW glass 237 Np radiotoxicity in environment Past use for 238 Pu production Future fuel cycles can burn Np in Pu/TRU fuels Current reprocessing by PUREX process Np is split across several streams Requires extra SX cycle to decontaminate Advanced reprocessing direct Np to single stream Reduced costs, wastes Enhance proliferation resistance

7 Np redox chemistry in HNO 3 NpO 2 2+ NpO NO H... Disproportionation NpO 2 + HNO 3 / HNO 2... NpO HNO H 2 O 2NpO 2 4H Np 4 NpO 2 2 2H 2 O HNO 3 / HNO 2 Np 4+ 3 easily inter-convertible oxidation states in HNO 3

8 Np(V) Rel. Abs. Np(V) oxidation vs. Np(VI) reduction in HNO HNO 2 added catalyses Np(V) oxidation Addition of 1 mm NaNO2 No HNO 2 to catalyse the redox reaction HNO 2 added reduces Np(VI) Np(V)/Np(VI) equilibrium position defined by HNO 3 /HNO time (min.) No HNO 2 to catalyse the redox reaction Np(VI) with 1 mm NaNO2 Np(V) zero nitrite Np(V) with 1mM NaNO2 Np(VI) zero nitrite Reduction of Np(VI) and oxidation of Np(V) in 5 M HNO 3 at 50 o C with and without NaNO 2

9 Np extraction in PUREX D Np [ Np] [ Np] organic aqueous D(NpVI) > D(NpIV) > D(NpV) Np(VI) = very extractable Np(IV) = extractable Np(V) = not extractable Need to stabilise the middle oxidation state

10 Conventional PUREX process ~70 % Np HNO 3 U IV /N 2 H 4 1BXX 35 C 1C 50 C HAF HS 50 C HA 35 C U IV /N 2 H 4 1BX 35 C 1BS HNO 3 U IV /N 2 H 4 Condition 20% TBP 20% TBP UP1 25 C 25 C UP2 50 C HAN U Finishing UP3 40 C HNO 3 HAN HAN HNO 3 HAR 30% TBP Diluent wash Condition PP1S 45 C PP2 30% TBP HA Feed PP1E 45 C Diluent wash Condition Concentrate Finishing 30% TBP ~30 % Np How can we achieve 100 % extraction in future SX processes? -pulsed columns -centrifugal contactors

11 Advanced PUREX process Dissolved SNF Extract/scrub HLW (Am,Cm,FPs) Np follows U,Pu Simplified PUREX process Single cycle SX flowsheet Np control In a single stream With Pu-U product With U then separated U/Pu separation Np barrier U backwash Option A. Np follows Pu Option B. Np follows U A1: Pu,Np A2:Pu,U,Np B: Np U Minor actinide (Am,Cm) separations require additional SX cycles on HLW

12 GANEX Process Dissolved SNF Co-separation of all TRU actinides U extraction An + Ln extraction An stripping Ln stripping U FPs Pu, Np, Am, Cm Ln GANEX 1 st cycle GANEX 2 nd cycle

13 PUREX vs. GANEX processes SX from nitric acid into an organic kerosene phase Different extracting ligands PUREX TBP O O P O O U Pu Np EURO-GANEX O O TODGA C 8 H 17 C 8 H 17 DMDOHEMA H 3 C N N CH 3 C 8 H 17 N O O O N C 8 H 17 C 8 H 17 U Pu Np Am Cm C 2 H 4 O C 6 H 13 C 8 H 17

14 Np extraction depends on HNO 3 HNO 2 Extraction of HNO 2 and Np(VI) into solvent U saturation of the solvent Chemical kinetics in aqueous and organic phases Temperature Any other redox active species Residence time in contactor Mixer-settlers > pulsed columns > centrifugal contactors Common problem to Advanced PUREX & GANEX processes

15 Np extraction in Advanced PUREX Experiments increasing in complexity Single phase, 2-phase, single centrifugal contactor stage Flowsheet trial Modelling See talk by Hongyan Chen! The Np(V) oxidation reaction is promoted by Conditions in aqueous solution High [HNO 3 ], [HNO 2 ]/[Np](aq) ~ 2, T = 50 C U loading reduces D(HNO 2 ) Within a flowsheet need to consider: Sufficient [HNO 2 ] in regions of low [U] during extraction Increase [HNO 3 ] across the extract section Elevated temperature around the extract and scrub section

16 NNL Np extraction flowsheet test SP1 FC1 A2 S1 HEATER HEATER 1 HS1 4 5 HA1 8 9 HA HA3 14 A1 HAF AR1 F1 F2 Miniature centrifugal contactors Simulant feed U+Np No hot test yet

17 CEA Np extraction test HNO 3 HAF S HNO 3 SP U,Np,Pu Spent fuel test LWR UOx fuel Pulsed columns E2 E1 HNO 2 X 30% TBP HAR <0.11 % Np 30% TBP AR <0.25 % Np Dinh, B., et al. in Solvent extraction: fundamentals to industrial applications. Proceedings ISEC 2008 International Solvent Extraction conference pp (2008).

18 Key results 2 successful tests NNL >99 % Np extracted U/Np test HNO 2 added No radiation field HM ~ 250 g/l Centrifugal contactors Lab scale Heated to 50 C (stages 1-8) 4.5 mol/l HNO 3 feed CEA >99.6 % Np extracted Spent fuel test No HNO 2 feed required Radiolytically generated HNO 2 HM ~250 g/l Pulsed columns Pilot scale Ambient temperature 4.5 mol/l HNO 3 feed

19 Np extraction in GANEX D Np 1.E+04 D Np 1.E+03 Np(IV) 0.2M TODGA Np(VI) 0.2M TODGA Np(IV) 0.5M DMDOHEMA Np(VI) 0.5M DMDOHEMA 1.E+03 Np(IV) Np(VI) Np(V) 1.E+02 1.E+01 1.E+02 1.E+00 1.E+01 1.E+00 1.E [HNO 3 ] aq,ini (M) 1.E-01 GANEX: Np(IV)>>Np(VI)>>Np(V) 1.E [HNO 3 ] aq,ini (M) Np(IV): TODGA>DMDOHEMA Np(VI): DMDOHEMA>TODGA Np(V) more extractable than PUREX

20 Absorbance Optimising Np extraction Stability Np(IV)>Np(VI)>>Np(V) Promote extraction by promoting Np(V) disproportionation in flowsheet 0.3 Np(IV) Np(V)+(IV) minutes following extraction 17 hours following extraction at RT Np(IV)+(VI) Np(VI) in DMODHEMA Initial aq. = 5 M HNO Wavelength (nm)

21 Np(V) disproportionation Redox reaction residence time dependent Faster in organic phase than aqueous phase Faster in GANEX solvent than PUREX solvent Rate increases with increased nitric acid concentration and temperature Kinetic equation derived in 30 % TBP Products Np(IV,VI) are both extractable Promoting disproportionation should promote extraction

22 EURO-GANEX process tests Solvent Feed Actinides Lanthanides Extract Scrub 16 FPs Active feed 5.9 M HNO M CDTA SF solution (10 g/l Pu) 0.5M HNO 3 Solvent Raffinate 32 Ln Strip 29 Loaded Solvent Feed An Strip 17 Solvent Feed 0.01M HNO 3 Lanthanides 0.5M HNO 3 1M AHA 0.055M BTP Pu, Np, Am, Cm

23 Flowsheet results Glovebox test (NNL) Hot cell test (ITU) Contactors Centrifugals Centrifugals Feed Surrogate Fast reactor spent fuel Pu content in feed (g/l) Pu recovery in E/S (%) > Am recovery in E/S (%) > Np recovery in E/S (%) ~ Np in HAR (%) ~ 29 Np in TRU product (%) ~

24 Conclusions & outlook Np control is one of main chemistry challenges for advanced reprocessing Affects plant layout, economics, waste management, proliferation resistance, corrosion Complex chemistry in nitric acid and organic phases Extraction is residence time dependent Now demonstrated that complete extraction is achievable by adjustment of acidity and temperature In advanced PUREX flowsheets In EURO-GANEX flowsheet & with short residence time centrifugal contactors Enhanced extraction under HA conditions (with SNF) Predictive & mechanistic based models now required

25 Acknowledgments NNL Signature Research programme in Spent Fuel and Nuclear Materials EU Framework VII project ACSEPT Sellafield Ltd. UK Nuclear Decommissioning Authority Chris Maher, Chris Mason, Katie Bell, Jamie Brown, Mark Sarsfield, Zara Hodgson (NNL), Helen Steele (NNL/CEA) Danny Fox, Cécile Roube, Gill Crooks, Chris Jones, Eddie Birkett (ex-nnl) ACSEPT project Andreas Geist (KIT), Rikard Malmbeck (ITU), Giuseppe Modolo, Andreas Wilden (FZJ), Xavier Hères, Stéphane Bourg, Manuel Miguirditchian (CEA) Colin Boxall, Scott Edwards (Lancaster University) Megan Jobson, Hongyan Chen, Andrew Masters (University of Manchester) Key references 1. M. J. Carrott, et al. Neptunium extraction and stability in the GANEX solvent (0.2 M TODGA / 0.5 M DMDOHEMA / kerosene), Solv. Extr. Ion Exch. 31, (2013). 2. R. J. Taylor et al. Progress towards the full recovery of neptunium in an Advanced PUREX process, Solv. Extr. Ion Exch. 31(4) (2013). 3. C. Gregson et al. Neptunium (V) oxidation by nitrous acid in nitric acid, Procedia Chemistry, 7, 2012,